In Part 11 of my series on the making of the Wall-Saver safety cylinder, I discussed the making of the plastic inserts that hold the brass plungers in place. Having figured out how to make them reliably, there remained the matter of inserting the plastic and brass, with oversized lip, into the cylinders.
Early experiments had shown that the way to do this successfully was to use the extractor star to complete the chamber, and a machinist’s vise (one of the tiny Sherline versions of that tool) to have nice parallel faces to press it in with. Some of the lip usually peeled off, but it did work much of the time. But, as has happened so many times before, the defect rate was too high. Sometimes the insertion process would cause a bulge in the cylinder that would jam it when it was put on the gun. Sometimes the plastic insert would get canted to one side and deformed. Sometimes the brass would get jammed and refuse to budge. It didn’t happen every time, but 1 out of 5 chambers was enough to cause a reject.
The hard polyurethane used for my cylinders is excellent for durability and fit, but one thing it is not is resilient. It tends to deform permanently or break under stress. (Nylon would actually be a better choice in some ways, but that would have called for an injection mold, and any mold suitable for making a revolver cylinder is going to be very complicated, and very expensive.) So my first experiment was to try a softer plastic. That was a complete failure, and if anyone needs a couple pounds of polyurethane, you can have it. It was softer, yes, but it was not more resilient, merely more eager to deform permanently.
Now I was getting frustrated, because I wasn’t sure what was going to make this whole thing work. So I went back to the design and discovered something mysterious and dumb. In my first experiments (discussed in Part 4 and Part 5), I had made a lip about .010” wide. But for some reason when I drew up the new CAD model, the lip was .020” wide! It was another moment of “What was I thinking?” So I re-made the toolpaths for the hard mold and made a new one. Unfortunately it came out with a lip .015” wide, but having done it…it seemed to work. No more bulging.
Now it was time to swing in to production in earnest.
Leave a Reply